I know scriptures encourage to marry within the same Varṇa (especially a female marrying a lower Varṇa), but these always seemed to me to be about people seeking marriage, not wanting to marry someone specific. I especially believe this I think I remember Bhīṣma saying a man should marry a women three years younger than him, which is obviously meant for people looking for a spouse they have met yet from literally no one reacting to marriages that don't have this age combination and this being very impractical to be a hard rule. There also does not seem to be any repercussions for marrying outside your Varṇa, which would be expected if this wasn't just dating advice.
Is there anything in scripture that is against marriage across Varṇa, and it definitely cannot be explained by just being dating advice i.e. doesn't allow marriage from falling in love unintentionally?